The Ce3+/Ce4+ redox potential changes with the electrolyte, which could be due to unequal anion coniplexation free energies between Ce3+ and Ce4+ or a change in the solvent electrostatic screening. Ce cornplexation with anions and solvent screening also affect the solubility of Ce and charge transfer kinetics for electrochemical reactions involving waste remediation and energy storage. We report the structures and free energies of cerium complexes n seven acidic electrolytes based on Extended X-ray Absorption Fine Structure, LTV vis, and Density Functional Theory calculations. Ce3+ coordinates with nine water molecules as [Ce(H2O)(9)](3+) in all studied electrol)rtes. However, Ce4+ complexes with anions in all electrcilytes except HClO4. Thus, our results suggest that Ce4+ anion comicilexation leads to the large shifts in standard redox potential. Long range screening effects are smaller than the anion complemation energies but could be responsible for changes in the Ce solubility with acid.